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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>
        // let arr = [1, 2, 3]
        // let a = arr[0]
        // let b = arr[1]
        // let c = arr[2]
        // let d = arr[3]
        // console.log(a,b,c,d);
        // let [a,,,b]=arr
        // console.log(a,b);// 1  un
        // let [a,...b]=arr
        // console.log(a, b); //1 [2,3]
        // let [...a]=arr
        // console.log(a);// [1,2,3]
        // let [a]=[]    
        // console.log(a);  //un
        // let [a]=[null]
        // console.log(a);  //null
        // let [a=1] = [null]
        //     console.log(a);  //null
        let [a=1] = [undefined]  
            console.log(a);  //1 
    </script>
</body>

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